Heretofore, in a light-emitting diode (LED) device, an organic material such as a resin has been used as a covering material to seal or cover a LED element and a substrate supporting such a LED element (hereinafter generally referred to as a “LED assembly”. However, a problem has been pointed out such that the covering material made of a resin is susceptible to deterioration by heat formed during the operation of the LED device, light and/or the environmental moisture, and its useful life is short.
Therefore, for covering a LED assembly, it has been studied to use a covering material made of glass which is more stable as compared with a resin. However, if conventional common silicate glass is used as a coating material for a LED assembly, a covering treatment temperature of about 500° C. or higher is required from the restriction of the glass softening point. For various components constituting a LED device, covering treatment at such high temperature is not desirable from the viewpoint of the reliability. In order to employ glass as a covering material, glass is required which is capable of carrying out covering treatment of a LED assembly at a covering treatment temperature of less than 500° C., particularly at most 400° C.
Further, Patent Document 1 discloses tin phosphate type glass having at least one of R2O (wherein R is Li, Na and/or K), B2O3, Al2O3, SiO2 and WO3 added, to form fusion seal between electronic or electric components.